title: Lymphoma presenting as a popliteal mass in a patient with rheumatoid arthritis.
abstract: A patient with HLA-B27 and rheumatoid factor positive rheumatoid arthritis presented with a painless swelling in his popliteal fossa. Clinical features were atypical for a Baker's cyst, and subsequent investigation showed this lesion to be a primary malignant lymphoma.
authors.affiliation: University of Toronto Rheumatic Disease Unit, Department of Orthopaedic Surgery, Toronto, ON, Canada.
authors.forename: J D
authors.initials: JD
authors.lastname: de Beer
authors.forename: E R
authors.initials: ER
authors.lastname: Bogoch
authors.forename: H A
authors.initials: HA
authors.lastname: Smythe
mesh_terms: D001172:Arthritis, Rheumatoid / Q000150:complications* / Q000276:immunology / Q000473:pathology; D003937:Diagnosis, Differential; D015796:HLA-B27 Antigen / Q000276:immunology; D006801:Humans; D008223:Lymphoma / Q000150:complications / Q000175:diagnosis* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D011151:Popliteal Cyst / Q000150:complications / Q000175:diagnosis* / Q000473:pathology; D012217:Rheumatoid Factor / Q000276:immunology
chemical_list: D015796:HLA-B27 Antigen; D012217:Rheumatoid Factor